The main objectives of this research program are to determine what functional neuronal subsets make up sensorimotor cerebral cortex of the domestic cat, how the different subsets interconnect to form "circuits," what thalamic inputs innervate each subset, and what subsets send information to what subcortical sites. They also are to determine what subsets are involved in different evoked potentials, what their relative timing is in the different potentials, and how this neuronal activity generates the patterns of net vertical current flows and surface voltage changes observed. To attain these objectives, the response properties of large samples of single neurons are recorded via extracellular microelectrodes during experimental maneuvers designed to characterize them functionally, and during different "spontaneous" and evoked potentials, especially the primary evoked response, augmenting and recruiting potentials. Through methods of population analysis, the basic circuitry of the tissue is determined and tested, and the characteristics of its operation during each of the evoked potentials is analyzed. Variations of the basic "cicuitry" are examined, and the possible modular arrangement and spatial distribution of the modules -columns, bands, gradients - are analyzed. For each potential, the pattern of net vertical current flow is calculated from the rate of change of the voltage field through depth in the tissue. The relationship of these patterns of current flow to the associated patterns of neuronal activity is then studied quantitatively, and the relationship of each to the surface-recorded potential is determined. From these studies, the detailed composition, organization and operation of sensorimotor cortex, and whether it has two preferred modes of operation, can be determined. To aid in attaining these objectives, a fully automated research program is used. A computer-controlled microdrive is directed by the main program to advance the electrode until a single neuron responsive to the hunting stimulus is automatically detected, isolated, and identified. A predefined, dynamically altering experiment is then performed on the neuron. Appropriate stimuli are delivered under computer command; data are acquired by the computer and immediately analyzed. Data flow/animal is significantly higher than with manual techniques.